fix: assimp INCOMPLETE flag no longer rejects animation-only FBX

Assimp flags every mesh-less scene as AI_SCENE_FLAGS_INCOMPLETE
(FBXConverter), so pure animation FBX never reached clip parsing -
the scene was discarded before ParseAnimations ran. Only treat null
scene / missing root node as hard failure; log INCOMPLETE as a
warning and continue. Final validity stays with ParsedModel::Valid().

Engine/src/Renderer/Model.cpp

@@ -193,22 +193,21 @@ ParsedModel Model::ParseFromDisk(const std::string& path)
         aiProcess_JoinIdenticalVertices |
         aiProcess_LimitBoneWeights);   // 每顶点限 4 权重（= 顶点格式 boneIds 容量）
 
-    if (!scene || (scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE) || !scene->mRootNode) {
-        // scene 可能为 null（文件损坏/格式不支持），先判空再打印资产清单
-        if (scene != nullptr) {
-            ENGINE_WARN("Assimp warn: model dose not have mesh assets\nmodel has following asset:");
-
-            ENGINE_WARN("\tMeshes Count: {}", scene->mNumMeshes);
-            ENGINE_WARN("\tAnimations Count: {}", scene->mNumAnimations);
-            ENGINE_WARN("\tCameras Count: {}", scene->mNumCameras);
-            ENGINE_WARN("\tLights Count: {}", scene->mNumLights);
-            ENGINE_WARN("\tMaterials Count: {}", scene->mNumMaterials);
-            ENGINE_WARN("\tSkeletons Count: {}", scene->mNumSkeletons);
-            ENGINE_WARN("\tTextures Count: {}", scene->mNumTextures);
-        }
-        ENGINE_ERROR("Assimp error: {}", importer.GetErrorString());
+    // 硬失败只有两种：scene 为 null（文件损坏/格式不支持）、无根节点。
+    // 注意 INCOMPLETE 不能当失败判据——assimp 对"无网格场景"统一打此
+    // 标记（FBXConverter：没读到 mesh 就置位），纯动画 FBX 必中，数据
+    // 本身完好。继续解析，最终有效性由 Valid()（mesh 或 clip 至少
+    // 其一非空）统一裁决
+    if (!scene || !scene->mRootNode) {
+        ENGINE_ERROR("Model parse failed: '{}' ({})",
+                     path, importer.GetErrorString());
         return out;   // meshes/clips 空 = 无效
     }
+    if (scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE) {
+        ENGINE_WARN("Assimp: no meshes in '{}' (anims: {}, materials: {}) "
+                    "- continuing for animation data",
+                    path, scene->mNumAnimations, scene->mNumMaterials);
+    }
 
     // 骨骼动画三件套：node 表（global 累乘骨架）→ 动画轨道 → 骨骼注册
     //（DFS 序；ProcessNode 的 mesh 遍历序与其独立，nodeIdx 靠 name 查表）